1. Field of the Invention
This invention lies in the field of winding of fibres. The broad sphere of application of the invention is to the winding of any form of fibre, filament, cord or any analogous structure. The invention is furthermore applicable to the winding of such fibre for any purpose.
2. Prior Art
In the field of large diameter, high pressure pipes, people have for some time looked into the possibility of manufacturing pipes from reinforced plastics. The idea was to combine the high corrosion, abrasion and crack resistance of many plastics with the high tensile strength of all sorts of fibres, especially the cheap glass fibres, which combine a very high ultimate tensile strength with a practically equally high yield strength. The glass fibre does show practically no creeping even under strong load.
In the case of pipes for pipelines with a high internal pressure the stress directions are practically circumferential and axial. For a maximum reinforcement effect one therefore has to wind in layers of endless circumferential fibres (rovings), and provide axial fibres.
For continuous pipe production by extrusion one needs a device that provides axial and circumferential fibres (rovings) continuously without any interruption. This is especially important with any process combined with a pipe extruder, since any stopping of the extruder causes deterioration of the extruded material.
In the case of small extruded pipes big, quickly rotating discs with spools are used to put the circumferential fibres on while the axial fibres are drawn from a standing spool bank into the protruding extruded material. Naturally, the spool discs have to be stoppped from time to time to put new spools on with a resulting interruption in the extrusion process.
For a given inside pressure the quantity of required endless fibres in the laminate per unit pipe length grows quadratically with the pipe diameter, as does the mass of the extruded material. Since the material wasted inside the extruder with each stop grows cubically with the extruder size and the pipe length manufactured in one shot decreases quadratically with the pipe diameter for a given rotating disc, the extruded material waste portion grows at least with the fourth power of diameter. The spool disc device is therefore rendered absolutely impractical for pipe diameters over 100 mm. U.K. Pat. Nos. 1 191 711 and 988 789 describe machines which are subject to similar shortcomings.
As a compromise short glass fibres are nowadays worked into the polymerisate and, together with the thermoplast, extruded. This approach, however, attains only a small fraction of the strength attainable by reinforcement with endless fibres. At the same time it requires very expensive extruder dies made from exotic, highly alloyed steel to withstand the high abrasion, caused by the short glass fibres, even for a very limited time.
In the Drostholm process use is made of continuous filament winding procedure with resin added to the wound fibre. The mandrel, on which the fibres are wound, consists of a parallel helically wound, endless steel tape. At the end of the "mandrel" the endless tape disappears into the rotating helical pipe appearing at the other end of the helix and starting the cycle again. This process shows three disadvantages:
(a) In the axial direction only short glass fibres can be brought in more or less at random; PA0 (b) Only a low winding speed is possible since centrifugal forces tend to cast out the resin; PA0 (c) The machine is expensive and complicated. The helical mandrel is only accessible after dismantling the machine.
So even in the field of directly setting (duroplastic) resins further improvements on pipe manufacturing should be found to allow for the mass production of highly reinforced pipes with circumferential and axial endless straight fibres.
The common point of the foregoing deficiencies lies in the fact that with every type of winding process which makes use of a rotating set of fibres, it was thought to be necessary to rotate the spool bank and the mandrel relatively to each other. The innovation below will show that this is not necessarily true. It thus opens a completely new field in high speed, continuous, endless fibre reinforcement of pipes, sheets, profiles and all types of containers.